Leakage current detection and interruption circuit with improved shield

ABSTRACT

A circuit is disclosed for disconnecting a power source upon the detection of a leakage current comprising a power cable having an insulated first and a second wire. The power cable has a conductive shield surrounding the first and second wires with a drain wire electrically contacting the conductive shield. A disconnect switch is interposed between the power source and the power cable. A primary circuit controls the disconnect switch. A secondary circuit is connected to the drain wire for sensing a leakage current between the conductive shield and one of the first and second wires. An optical switch interconnects the primary circuit and the secondary circuit for opening the disconnect switch upon the secondary circuit sensing a leakage current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.11/324,087 filed Dec. 30, 2005. U.S. patent application Ser. No.11/324,087 filed Dec. 30, 2005 claims benefit of U.S. Patent Provisionalapplication Ser. No. 60/641,187 filed Jan. 4, 2005. All subject matterset forth in application Ser. No. 11/324,087 and application Ser. No.60/641,187 is hereby incorporated by reference into the presentapplication as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to electrical power circuit and more particularlyto a circuit for disconnecting a power source upon the detection of aleakage current.

2. Background of the Invention

Various types of electrical protective devices have been proposed by theprior art for reducing the possibility of dangerous electrical shocks aswell as the possibility of electrical fires. One general class of priorart electrical protective devices is a commonly referred to as a groundfault circuit interrupter (GFCI). A ground fault circuit interrupterdisconnects a power source upon the detection of an undesired groundingof a power line, such as by a person inadvertently being connectedbetween the power line and a ground. Other types of types of electricalprotective devices include appliance leakage current interrupters(ALCIs), equipment leakage current interrupters (ELCIs) and immersiondetection circuit interrupters (IDCIs). Underwriters Laboratories, Inc.classifies electrical protective devices as Leakage Current ProtectionDevices, in Reference Standard UL943A. The following United Statespatents are representative of leakage current protection devices of theprior art.

U.S. Pat. No. 4,131,927 to Tsuchiya, et al. discloses a current surge,normally associated with the initial application of a nominal A.C.current to an inductive load, for preventing the magnetic core of theinductive load from being driven into saturation. Initially, the currentis half wave rectified and amplitude limited. The amplitude limitationinsures that the core will not be driven into saturation. A voltagedetector connected across the inductive load senses only the counterE.M.F. of a polarity opposite to the polarity of the half wave current.When the sensed voltage reaches a predetermined value, a directconnection is provided between the A.C. supply and the inductive load,bypassing the half wave rectifier and the amplitude limiter.

U.S. Pat. No. 4,352,998 to Baker, et al. discloses a common moderejection coupler in a power switching system having a variable commonmode voltage including a first optical isolator circuit for receiving aninput signal and generating in response thereto a first signal which isnormally isolated with respect to the common mode voltage. A secondoptical isolator circuit receives the complement of the input signal andgenerates a second signal which is also normally isolated with respectto the common mode voltage. The first and second signals are thecomplement of one another. A comparator receives the first and secondsignals and generates an output signal which changes state only when thefirst and second signals complement states. Feedback control circuitryfor the comparator is provided for limiting transient changes in one ofthe first and second signals to prevent the comparator from changingoutput states when a transient change occurs in one of the first andsecond signals resulting from a change in the common mode voltage.

U.S. Pat. No. 4,424,544 to Chang, et al. discloses an optically toggledbidirectional normally-on switch with protection against bilateralvoltage and bidirectional current surges by the inclusion of a pair ofoppositely poled thyristors. One version uses a large junction-typefield-effect transistor in its main path and a pair of smallerjunction-type transistors in the subsidiary path. A photodiode arraycontrols the gate voltage on each of the transistors and turns them offwhen illuminated. A control node in the subsidiary path is connected tothe gates of the SCRs so that excess current in this path turns on theappropriately-poled thyristor to provide an additional shunt path forthe current.

U.S. Pat. No. 4,554,463 to Norbeck, et al. discloses a trigger circuitfor gating on a semiconductor switch. The power dissipated in thetrigger circuit is minimized by employing a constant current source toprovide the gate trigger current. This assures adequate triggeringregardless of supply voltage variations or switch intrinsic controlvoltage requirements. Power is saved by supplying only the currentrequired to drive the semiconductor switch on thereby preventingoverdrive. With constant d-c gate current, the precise amount of powerneeded to turn on and close the switch is provided while wastingrelatively little energy due to gate intrinsic voltage variations of theswitch or to input line voltage variations.

U.S. Pat. No. 4,717,841 to Dumortier, et al. discloses a static powerswitch circuit having a power switch member. The static power switch hasa bidirectional power switch with at least one controlled semiconductorof the thyristor or triac type with power terminals connected to an ACsource in series with a load and a circuit for controlling the powerswitch member having a first control switch whose current path isconnected to the gate of the power semiconductor through a full waverectifier bridge. This switch is connected to a circuit able to generatecontrol energy of the switch in response to an input signal.

U.S. Pat. No. 5,262,691 to Bailey, et al. discloses an apparatus forresponding to a shorted gate in a gate turnoff thyristor. The gateelectrode of which is connected by means of a controllable switch to acontrol voltage terminal having a negative potential with respect to thecathode potential of the thyristor. The controllable switch is arrangedto conduct negative gate current in response to a thyristor turnoffcommand. A voltage comparing means is coupled to the controllable switchfor detecting when the switch is conducting negative gate current ofrelatively high magnitude. Timing means is active for a predeterminedinterval following the start of the thyristor turnoff command, and logicmeans is operative to cause the switch to stop conducting negative gatecurrent if the voltage comparing means detects high gate current at theend of such interval.

U.S. Pat. No. 5,365,394 to Ibarguengoitia discloses a protectiveelectronic relay of the type which includes a feed source with aone-phase transformer, rectifying bridge, filter condenser and voltageregulator. Pickups are provided where one-phase signals are generated,connected to some diodes, connected to some capacitors and to a zenerdiode for the purpose of obtaining rectified, filtered and limitedsignals with a voltage level proportional to the line intensity of theprotected motor. A multiple microswitch connected to some resistorspermits presetting of the voltage level and nominal triggering intensityof a relay. An R-C network that can be timed in various scales comprisedof resistors a capacitor and another multiple microswitch allowsadjustment of the triggering time constant and is applied to thatvoltage level at the non-inverting input of an operational amplifierwhose inverting input is at a reference voltage. Upon the non-invertinginput of the operational amplifier reaching the reference voltage, dueto a symmetric overload, the output of the operational amplifier passesto logic state 1. This sends a positive signal to the gate of athyristor, driving it into conduction and depolarizing the base of atransistor making it pass from saturation to cut-off. As a result arelay connected to the collector of the transistor is triggered,changing the state of its contacts and causing disconnection of theprotected motor.

U.S. Pat. No. 5,418,678 to McDonald discloses an improved ground faultcircuit interrupter (GFCI) device requiring manual setting followinginitial connection to an AC power source or termination of a powersource interruption. The improved GFCI device utilizes a controlledswitching device which is responsive to a load power signal for allowingthe relay contact sets of the GFCI device to be closed only when poweris being made available at the output or load terminals. The controlledswitching device preferably comprises an opto-isolator or other type ofswitching device which provides isolation between the GFCI input andoutput terminals when the relay contact sets are open. The improved GFCIdevice may be incorporated into portable units, such as plug-in or linecord units, for use with unprotected AC receptacles.

U.S. Pat. No. 5,459,336 to Kato discloses a semiconductor photocouplercomposed of a light emitting element and a light receiving element.Wavelength of emitted light changes as a function of exciting currentintensity of the light emitting element, and capacitance of the lightreceiving element changes as a function of wavelength of receiving lightand ceases the capacity change as the receiving light disappears.Signals are transmitted in current-light-capacity type transmission withmemory action in the light receiving element.

U.S. Pat. No. 5,463,521 to Love discloses an apparatus for protectingelectronic circuit elements from hazardous voltages. The apparatusincludes a source of electrical energy that produces electrical energyhaving a predetermined energy level. An electrical load is connected tothe electrical energy source and responsively receives electricalenergy. A signaling device receives electrical energy from theelectrical energy source and produces an overvoltage signal in responseto receiving electrical energy greater than the predetermined energylevel. A NMOSFET is connected to the electrical load, and controllablyregulates the electrical current flowing through the electrical load. Acontrol device receives the overvoltage signal and responsively controlsthe operation of the NMOSFET.

U.S. Pat. No. 5,528,445 to Cooke, et al. discloses a fault currentprotection system for a traction vehicle propulsion system including asynchronous generator having armature and field windings and powerconditioning circuitry connecting the generator armature windings to atraction motor employing a normally charged capacitor which, in responseto a fault signal resulting from excess current in the generatorarmature windings, is electrically switched into parallel with theexcitation current source connected to the generator field windings soas to discharge through the generator field windings and commutate theexcitation current source.

U.S. Pat. No. 5,661,623 to McDonald, et al. discloses a ground faultcircuit interrupter (GFCI) line cord plug utilizing an electronicallylatched relay, rather than a circuit breaker or other type of mechanicallatching device, to interrupt the AC load power when a ground faultcondition occurs. In order to reduce the size of the relay and minimizethe cost and complexity of the GFCI plug, the fixed and movable relaycontact structures are mounted directly to the circuit board whichcarries the remaining components of the GFCI circuit. In a preferredembodiment, the fixed relay contact structures are integral with theplug blades of the GFCI plug. The movable relay contact structurespreferably comprise deflectable spring arms which are preloaded when therelay contacts are in the open position in order to control the contactgap, and which are deflected past the point of contact closure when therelay contacts are in the closed position in order to increase theclosing force. The principal electrical components of the GFCI plug,including the relay contacts, relay coil and sensing transformer, aremounted on the circuit board in a generally tandem or in-linearrangement in order to minimize the dimensions of the plug.

U.S. Pat. No. 6,002,563 to Esakoff, et al. discloses an improved plug-inpower module for providing a controlled amount of electrical power toone or more remote lighting fixtures or other load. The module isconfigured to sense a ground fault or other current imbalance at theload and, in response, both to trigger the module's circuit breaker toopen and to report the occurrence of such a ground fault to a centrallocation. The power module achieves these important functions withoutadding unduly to the module's complexity or size.

U.S. Pat. No. 6,218,647 to Jones discloses an ice and snow meltingsystem including at least one sensor configured for sensing atemperature or moisture associated with an ambient environment andproviding a signal indicative thereof. A heater for melting the ice andsnow includes a heater wire, a layer of insulation substantiallysurrounding the heater wire, and a conductive shield substantiallysurrounding the layer of insulation. A ground fault circuit interrupteris coupled with the shield of the heater. The ground fault circuitinterrupter detects a ground fault condition between the heater wire andthe conductive shield and provides a signal indicative thereof. Anautomatic controller is connected to the at least one sensor. Thecontroller includes heater control circuitry receiving each of thesensor signal and the ground fault circuit interrupter signal. Theheater control circuitry selectively controls operation of the heaterdependent upon the sensor signal and the ground fault circuitinterrupter signal.

U.S. Pat. No. 6,252,365 to Morris, et al. discloses a combinationcircuit breaker/motor starter including a circuit breaker trip unithaving a microprocessor and at least one removably connectable contactoror other functional module. The functional module is encoded with anidentifier, such that the microprocessor can determine the type offunctional module and appropriate configuration parameters, such as triptimes, for the particular application of the functional module. Power issupplied continuously to the trip unit during motor overload or shortcircuit conditions.

U.S. Pat. No. 6,404,265 to Guido, Jr., et al. discloses a triggercircuit for triggering a silicon device having a control terminal, wherethe silicon device is subject to variations in the intrinsic controlrequirements. The trigger circuit comprises a source of direct current(DC) supply voltage, and a DC-to-DC current mode Buck converter forconverting the supply voltage into an output DC current not subject toundesired variations due to variations in the supply voltage, the Buckconverter supplying to the control terminal a minimum current to turn onthe silicon device despite the variations in the intrinsic controlrequirements. The silicon device may comprise a silicon controlledrectifier (SCR) with a gate terminal, an anode terminal, and a cathodeterminal, and wherein the control terminal is the gate terminal, andwherein the variations in the intrinsic control requirements arevariations in the intrinsic gate-to-cathode control current and voltagerequirements.

U.S. Pat. No. 6,414,829 to Haun, el al. discloses a system for producinga simulated ground fault when arcing is present in an electricalcircuit. The system includes a sensor which monitors the electricalcircuit. An arcing fault detection circuit determines whether an arcingfault is present in response to the sensor and produces a trip signal inresponse to a determination that an arcing fault is present in theelectrical circuit. A ground fault simulator circuit produces asimulated ground fault in response to the trip signal.

U.S. Pat. No. 6,697,238 and U.S. Patent Application 20020145838 toBonilla, et al. disclose a GFCI that has secondary test switch contacts.In case closing of the primary test switch contacts fails to trip theGFCI, subsequent closing of the secondary test switch contacts resultsin a short circuit between the AC input terminals of the GFCI. The shortcircuit blows a fuse disposed on the line side of the GFCI. The blowingof the fuse disables the GFCI and/or provides an indication to the userthat the GFCI is defective.

U.S. Patent Application 20030202310 to George, et al. discloses a methodand apparatus for improving the fault protection of a monitor circuit bycoupling an input protection circuit to an output section. The inputprotection circuit may include a fusible device that limits or removes afault condition present at an input to the input protection circuit. Thefusible device may be, for example, a resettable positive temperaturecoefficient (“PTC”) device configured to limit the current passingthrough it to a predetermined level once it reaches a predeterminedtemperature. A resistive element may be thermally coupled to the PTCdevice to assist it reaching the predetermined temperature. The monitorcircuit may further be configured to generate a sensory signal inresponse to a fault condition.

U.S. Patent Application 20040037018 to Kim discloses a GFCI mis-wiringdetector including a set of input terminals for an AC source, and a setof output terminals for an AC load. The set of output terminals areconductively connected to the set of input terminals. A GFCI circuit hasone or more switches that selectively interrupt the connection betweenthe set of input terminals and the set of output terminals when a groundfault occurs. A mis-wiring detection circuit causes the one or moreswitches of the GFCI circuit to open when the AC source is electricallycoupled to the set of output terminals for a first time interval, evenif there is no imbalance in the current flow. Additionally, asuppression circuit suppresses operation of the mis-wiring detectioncircuit when the AC source is electrically coupled to the inputterminals for a second time interval. The second time interval is lessthan the first time interval.

U.S. Patent Application 20040070895 to Gershen, et al. discloses a SCR,which is used to fire a coil. The coil uses the ground conductor anddiodes as the return path to fire the coil to interrupt the voltage fromthe load. A fully shielded cord is used to detect a break in aconductor. An LED indicator in either the plug or the receptacle of theextension cord verifies that protection is available. A test button isprovided to test shield continuity and to verify proper circuitoperation.

U.S. Patent Application 20040070899 to Gershen, et al. discloses basicdetection and interruption components of an Immersion Detection CircuitInterrupter (IDCI), in combination with the line, neutral and shieldconductors of an extension or appliance cord provides a new improvedtype of detector. A Leakage Current Detector Interrupter (LCDI)interrupts current to a load when current leakage is detected betweenthe line or neutral conductors of the cord and the shield conductor. Thenew improved LCDI detector provides, either singularly or incombination, the following advantages: prevents the LCDI from beingreset should the device become inoperative (reset lockout); provides anindication of the integrity of the shield in the extension or appliancecord; tests the integrity of the shield within the extension orappliance cord, in addition to testing the functionality of the LCDI;interrupts current to the load if an electrical connection is detectedbetween the shield and neutral, or the shield and ground, in addition tothe existing detection of leakage current from the phase conductor,allows the LCDI to trip during an open neutral condition by utilizingthe ground connection as a return wire for the trip coil; and/orprovides immersion detection at the receptacle end of the extension cordin addition to protection from leakage faults.

U.S. Patent Application 20040190686 to Tidwell, et al. discloses anapparatus to determine whether or not protection circuitry for aspan-powered remote digital subscriber loop unit is properly connectedto earth ground by the deliberate assertion and detection of a groundfault from a central office line card location. The span-powered remoteunit is augmented to place a controllable conduction path in circuitwith the span-powered loop and an earth ground pin. If the earth groundpin has been properly connected to earth ground, applying the conductivepath will place a ground fault on the span, which is detected by aground fault detector within the central office line card. If the groundfault detector does not detect a ground fault in response to theapplication of the conductive path, the line card forwards a negativeground fault event message to a test center, so that a servicetechnician may be dispatched to the remote unit to correct the problem.

Therefore, it is an object of the present invention to provide a circuitfor disconnecting a power source upon the detection of a leakage currentthat provides a significant improvement in the electrical art.

Another object of this invention is to provide a further alternateembodiment from the inventions disclosed in my prior pending patentapplications set forth in the cross reference to related applications.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat completely isolates the power source upon the detection of aleakage current.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat utilizes an optocoupler for completely isolating the power sourceupon the detection of a leakage current.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat requires a reduced number of electrical components.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat incorporates an improved conductive shield for the detection of aleakage current.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat is more economical than similar units of the prior art.

Another object of this invention is to provide a circuit fordisconnecting a power source upon the detection of a leakage currentthat may be incorporated into existing line cord packages.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed as being merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be obtained bymodifying the invention within the scope of the invention. Accordinglyother objects in a full understanding of the invention may be had byreferring to the summary of the invention, the detailed descriptiondescribing the preferred embodiment in addition to the scope of theinvention defined by the claims taken in conjunction with theaccompanying drawings.

SUMMARY OF THE INVENTION

The present invention is defined by the appended claims with specificembodiments being shown in the attached drawings. For the purpose ofsummarizing the invention, the invention relates to a circuit isdisclosed for disconnecting a power source upon the detection of aleakage current comprising a power cable having an insulated first wireand an insulated second wire. The power cable has a conductive shieldsurrounding the insulated first wire and the insulated second wire witha drain wire being in contact with the electrical conductive shield. Adisconnect switch is interposed between the power source and the powercable with a primary circuit controlling the disconnect switch. Asecondary circuit is connected to the drain wire for sensing a leakagecurrent between the conductive shield and one of the insulated firstwire and the insulated second wire. An optical switch interconnects theprimary circuit and the secondary circuit for opening the disconnectswitch upon the secondary circuit sensing a leakage current.

In a more specific embodiment of the invention, the conductive shieldmay be a metallic foil such as an aluminum foil or may be a metallicmesh. In one example, the drain wire has a first and a second portionwith the first portion of the drain wire being non-insulated and incontact with the conductive shield. Preferably, the first portion of thedrain wire extends along substantially the total length of theconductive shield. In one example, the drain wire is located internal tothe conductive shield. In an alternate example, the drain wire islocated external to the conductive shield. The outer insulating layer ofthe power cable establishes a mechanical engagement between the firstportion of the drain wire and the conductive shield to provide anelectrical connection between the drain wire and the conductive shield.

In one example of the invention, the disconnect switch includes asolenoid operated switch. Preferably, the disconnect switch includes anormally closed solenoid operated switch and a latch for maintaining thedisconnect switch in an open condition upon the secondary circuitsensing a leakage current from the wire. In a specific example, thelatch comprises a mechanical latch mechanism for maintaining thedisconnect switch in an open condition upon the secondary circuitsensing a leakage current from the wire.

In another example of the invention, the secondary circuit includes alight emitting device connected to the drain wire for sensing a leakagecurrent between the conductive shield and one of the insulated firstwire and the insulated second wire. The light emitting device senses aleakage current between the wire and the shield sensing conductor.

The optical switch includes a light emitting device optically coupled toa photoconductive switch for completely electrically isolating the powersource upon the opening of the disconnect switch. The optical switchincludes a light emitting device electrically connected to the secondarycircuit for sensing a leakage current between the conductive shield andone of the insulated first wire and the insulated second wire. Aphotoconductive switch is connected to the primary circuit forcontrolling the disconnect switch. The light emitting device isoptically coupled to a photoconductive switch for electrically isolatingthe primary circuit from secondary circuit. In one example of theinvention, the optical switch includes an optocoupler switch having alight emitting device optically coupled to a photoconductive switch.

The circuit may be included with a housing molded from a polymericmaterial. In one example, the housing has a first and a second lug forinsertion within a first and a second socket. The power cable extendsfrom the housing.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed as being merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be obtained bymodifying the invention within the scope of the invention. Accordinglyother objects in a full understanding of the invention may be had byreferring to the summary of the invention, the detailed descriptiondescribing the preferred embodiment in addition to the scope of theinvention defined by the claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is an elevational view of the circuit of the present inventionconnecting a power source to a load shown as an air conditioning unit;

FIG. 2 is an enlarged view of the a portion of FIG. 1 illustrating anelectrical plug housing the circuit of the present invention;

FIG. 3 is a side view of FIG. 2;

FIG. 4 is a block diagram of the circuit of the present invention fordisconnecting an electrical power source upon the detection of a leakagecurrent;

FIG. 5 is an isometric view of a disconnect switch in a closed position;

FIG. 6 is an isometric view of the disconnect switch of FIG. 5 in anopen position;

FIG. 7 is a side sectional view of the disconnect switch of FIG. 5 inthe closed position;

FIG. 7A is a side view of the disconnect switch shown in FIG. 7;

FIG. 8 is a side sectional view of the disconnect switch of FIG. 5 in apartially open position;

FIG. 8A is a side view of the disconnect switch shown in FIG. 8;

FIG. 9 is a side sectional view of the disconnect switch of FIG. 5 in afully open position;

FIG. 9A is a side view of the disconnect switch shown in FIG. 9;

FIG. 10 is a side sectional view of the disconnect switch of FIG. 5illustrating the reset of the latch relay with the latch being in theopen position;

FIG. 10A is a side view of the disconnect switch shown in FIG. 10;

FIG. 11 is a side sectional view of the disconnect switch of FIG. 5illustrating the latch relay reset into the closed position;

FIG. 11A is a side view of the disconnect switch shown in FIG. 11;

FIG. 12 is a circuit diagram of a first embodiment of the circuit ofFIG. 4;

FIG. 13 is the circuit diagram of FIG. 12 connected to the circuit tothe power source;

FIG. 14 is the circuit diagram similar to FIG. 13 illustrating thedetection of a leakage current by the circuit;

FIG. 15 is the circuit diagram similar to FIG. 12 illustrating thedisconnection of the power source from the load;

FIG. 16 is the circuit diagram similar to FIG. 12 illustrating theoperation of a test circuit;

FIG. 17 is a circuit diagram of a second embodiment of the circuit ofFIGS. 1-4;

FIG. 18 is a circuit diagram of a third embodiment of the circuit ofFIG. 14;

FIG. 19 is a circuit diagram of a fourth embodiment of the circuit ofFIG. 14;

FIG. 20 is a circuit diagram of a fifth embodiment of the circuit ofFIG. 14;

FIG. 21 is a circuit diagram of a sixth embodiment of the circuit ofFIG. 14;

FIG. 22 is a circuit diagram of a seventh embodiment of the circuit ofFIG. 14;

FIG. 23 is a view of the electrical plug housing shown in FIGS. 1-3 withan alternate power cable extending from the housing;

FIG. 24 is an enlarged sectional view along line 2424 in FIG. 23 of thepower cable illustrating a first and a second wire, a ground wire andthe drain wire located within a conductive shield;

FIG. 25 is a view similar to FIG. 24 of a power cable with the drainwire located outside of the conductive shield;

FIG. 26 is a view similar to FIG. 24 of an alternate embodiment of apower cable illustrating a first and a second wire with a drain wirelocated within the conductive shield;

FIG. 27 is a view similar to FIG. 26 of a power cable with the drainwire located outside of the conductive shield;

FIG. 28 is a first example of a conductive shield suitable for use inpresent invention;

FIG. 29 is a second example of a conductive shield suitable for use inpresent invention;

FIG. 30 is a third example of a conductive shield suitable for use inpresent invention;

FIG. 31 is a fourth example of a conductive shield suitable for use inpresent invention;

FIG. 32 is a block diagram of an eighth embodiment of the presentinvention; and

FIG. 33 is a circuit diagram of the block diagram of FIG. 28.

Similar reference characters refer to similar parts throughout theseveral Figures of the drawings.

DETAILED DISCUSSION

FIG. 1 is an elevational view of the circuit 10 of the present inventionfor disconnecting a power source 15 upon the detection of a leakagecurrent. In this example, the power source 15 is shown as a conventionalelectrical receptacle 16. The conventional electrical receptacle 16 hasa line socket 17, a neutral socket 18 and a ground socket 19.

The circuit 10 is contained within a housing 20 in the form of anelectrical plug adapted for insertion within the conventional electricalreceptacle 16. A load 30 is shown as an air conditioning unit 32installed in a window 34. A wire assembly 40 connects the circuit 10within the housing 20 to the load 30.

FIGS. 2 and 3 are enlarged views of a portion of FIG. 1 furtherillustrating the circuit 10 contained within the housing 20. The housing20 supports a line lug 21, a neutral lug 22 and a ground lug 23. Thelugs 21-23 of the housing are adapted to be inserted into the sockets17-19 of the receptacle 16. Preferably, the housing 20 is formed from amolded polymeric material.

The circuit 10 connects the electrical lugs 21-23 to the wire assembly40 comprising a first and a second wire 41 and 42 and a grounding wire43. A first and a second insulation 44 and 45 surround the first andsecond wires 41 and 42 whereas insulation 46 surrounds the groundingwire 43 in a conventional fashion.

A first and a second shield 47 and 48 surround the first and second thefirst and second wires 41 and 42. As will be described in greater detailhereinafter, the circuit 10 disconnects the power source 15 from theload 30 upon the detection of a leakage current from any one of thefirst and second wires 41 and 42 and the first and second shields 47 and48. In addition, the circuit 10 disconnects the power source 15 from theload 30 upon the detection of a leakage current from the grounding wire43 to either one of the first and second shields 47 and 48. In thealternative, a conventional non-insulated wire (not shown) may extendalong the first and second wires 41 and 42 and the grounding wire 43 asa sensor wire for detecting a leakage current from the either one of thefirst and second wires 41 and 42 and/or the grounding wire 43.

FIG. 4 is a block diagram of the circuit 10 of the present invention fordisconnecting an electrical power source 15 from the load 30 upon thedetection of a leakage current within the wire assembly 40. In thisexample, the electrical power source 15 is shown as a conventional 110volt alternating current (AC) power source. The first terminal 21 is theline terminal whereas the second terminal 22 is the neutral terminal.Although the electrical power source 15 has been shown as conventional110 volt alternating current (AC) power source, it should be appreciatedby those skilled in the art that the present invention may be adapted tovirtually any type of power source.

The circuit 10 comprises a disconnect switch 50 interposed within thefirst and second wires 41 and 42 for disconnecting the power source 15from the load 30. In this example, a latch 60 cooperates with thedisconnect switch 50 as will be described in greater detail hereinafter.

A primary circuit 70 is connected to the disconnect switch 50 forcontrolling the disconnect switch 50. The primary circuit 70 opens thedisconnect switch 50 upon the secondary circuit 80 sensing at leakagecurrent from one of the first and second wires 41 and 42.

A secondary circuit 80 is located between the disconnect switch 50 andthe load 30 for sensing a leakage current between the one of the firstand second wires 41 and 42 and the first and second shields 47 and 48.In addition, the secondary circuit 80 senses a leakage current betweenthe grounding wire 43 shown in FIGS. 2 and 3 and one of the first andsecond shields 47 and 48.

The first and second shields 47 and 48 function as shield sensingconductors for enabling the secondary circuit 80 for sensing a leakagecurrent between the one of the first and second wires 41 and 42 and thefirst and second shields 47 and 48. In the alternative, a singlenon-insulated wire may be provided as a sensing conductor as shown inFIG. 18 for sensing a leakage current from either one of the first andsecond wires 41 and 42.

An optical switch 90 interconnects the primary circuit 70 and thesecondary circuit 80 for opening the disconnect switch 50 upon thesecondary circuit 80 sensing a leakage current within the wire assembly40 for completely electrically disconnecting the power source 15 fromthe load 30 and completely electrically disconnecting the primarycircuit 70 and the secondary circuit 80.

FIGS. 5 and 6 are isometric views of an example of the disconnect switch50 of FIG. 4 shown in a closed and an open position, respectively. Inthis example, the disconnect switch 50 comprises a first and a secondswitch 51 and 52 shown as resilient relay contacts 51 and 52 mounted onresilient metallic conductors 53 and 54. The resilient metallicconductors 53 and 54 bias the first and second switches 51 and 52 intoan open position.

FIGS. 7-11 illustrate various positions of the operation of thedisconnect switch 50 and the latch 60. An insulating switch operator 55interconnects the first and second switches 51 and 52 for moving thefirst and second switches 51 and 52 in unison. The insulating switchoperator 55 includes an aperture 56 defining a shoulder 57. Thedisconnect switch 50 includes a solenoid coil 58 for operating a plunger59. The plunger 50 is located for movement adjacent to the aperture 56in the insulating switch operator 55.

In this example, the latch 60 is shown as a mechanical latch comprisinga reset button 62 having a return spring 64. The resent button 62extends from the housing 20 as shown in FIGS. 1 and 2. A latch bar 66having a latch shoulder 68 is connected to the reset button 62.

FIGS. 7 and 7A illustrate the disconnect switch 50 of FIG. 5 in theclosed position. The latch shoulder 68 of the latch bar 66 engages withthe shoulder 57 defined by the aperture of the switch operator 55. Thereturn spring 64 is selected to be stronger than the resilient metallicconductors 53 and 54 biasing the first and second switches 51 and 52into an open position. The return spring 64 retains the first and secondswitches 51 and 52 in the closed position against the urging of theresilient metallic conductors 53 and 54.

FIGS. 8 and 8A illustrate the disconnect switch 50 in a partially openposition. An electrical current through the solenoid coil 58 extends theplunger 59 to displace the latch bar 66. The plunger 59 displaces thelatch bar 66 to disengage the latch shoulder 68 of the latch bar 66 fromthe shoulder 57 of the switch operator 55. The disengagement of thelatch shoulder 68 from the shoulder 57 permits the resilient metallicconductors 53 and 54 to bias the first and second switches 51 and 52into the open position.

FIGS. 9 and 9A is a side sectional view of the disconnect switch 50 in afully open position. The resilient metallic conductors 53 and 54 urgethe first and second switches 51 and 52 into the open position. Thefirst and second switches 51 and 52 remains in the open position untilthe disconnect switch 50 is manually reset.

Concomitantly therewith, the return spring 64 moves the reset button 62into an extended position. The resent button 62 extends from the housing20 as shown in FIGS. 1 and 2. The latch bar 66 and the latch shoulder 68move in unison with the reset button 62.

FIGS. 10 and 10A illustrate the movement of the reset button 62 by anoperator to reset the disconnect switch 50. The reset button 62 isdepressed against the urging of the return spring 64. The latch shoulder68 of the latch bar 66 reengages with the shoulder 57 of the switchoperator 55.

FIGS. 11 and 11A illustrate the fully reset disconnect switch 50. Thereturn spring 64 moves the first and second switches 51 and 52 into theclosed position against the urging of the urging of the resilientmetallic conductors 53 and 54.

Although the disconnect switch 50 has been shown as a normally open,latch closed solenoid mechanism, it should be appreciated by thoseskilled in the art that various types of mechanical and or electricalswitches may be utilized within the present invention for providing thestructure and function of the disconnect switch 50.

FIG. 12 is a circuit diagram of a first embodiment of the circuit 10 ofFIG. 4. The first and second terminals 21 and 22 extending from thehousing 20 are connected to the wires 41 and 42 of the wire assembly 40.A surge suppressor shown as a metal oxide varistor 26 is connectedacross the first and second wires 41 and 42. The function and operationof the metal oxide varistor 26 should be well known to those skilled inthe art.

The disconnect 50 is interposed within the wire assembly 40 with thefirst and second switches 51 and 52 located within the first and secondwires 41 and 42. The disconnect switch 50 is shown in the closed orreset condition.

The primary circuit 70 is located on a primary side of the disconnectswitch 50 for controlling the disconnect switch 50. The primary circuit70 opens the disconnect switch 50 upon the secondary circuit 80 sensinga leakage current from one of the wire 41 and 42. The disconnect switch50 is controlled through the solenoid coil 58 by the primary circuit 70.A diode 68 providing power through the solenoid coil 58 of thedisconnect switch 50 to a conductor 69 to power the primary circuit 70.The solenoid coil 58 is connected to a voltage divider network 71comprising resistor 72 and resistor 73. A capacitor 75 is connectedacross the resistor 73 of the voltage divider network 71. The conductor69 is connected to a switch shown as a thyristor or silicon controlledrectifier 76.

The voltage divider network 71 is connected to the collector of thephototransistor 91 of the optocoupler 90. A coil 77 connects the emitterof phototransistor 91 to the gate of the thyristor 76. A pull downresistor 78 and a capacitor 79 are connected to the gate of thethyristor 76.

The secondary circuit 80 comprises resistor 81 and 82 forming a voltagedivider network 83. The voltage divider network 83 is connected to lightemitting diodes 92 and 93 within the optocoupler 90. A connector 84connects the light emitting diodes 92 and 93 to the shield 48surrounding the second wires 42. A connector 85 connects the shield 48surrounding the second wire 42 to the shield 47 surrounding the firstsecond wire 41.

An optional test circuit 100 may be included for testing the circuit 10.The optional test circuit 100 comprises resistor 101 connected to thewire 42 of the wire assembly 40. A momentary switch 102 connects theresistor 101 to the shield 47 surrounding the first second wire 41through a conductor 103.

FIG. 13 is a diagram of the circuit 10 of FIG. 12 connected to the powersource 15. Power is applied to the circuit 10 by inserting the first andsecond terminals 21 and 22 extending from the housing 20 into theelectrical receptacle 17 shown in FIG. 1. Upon the application of power,conventional current flows from diode 68 through the solenoid coil 58 tothe voltage divider network 71. The diode 68 in combination withsolenoid coil 58 provides a direct current (DC) voltage for the primarycircuit 70.

The conductor 69 applies power to the voltage divider network 71 and tothe anode of the thyristor 76. The capacitor 75 assists in reducingalternating current (AC) voltage ripple within the voltage dividernetwork 71. The voltage divider network 71 provides operating voltage tothe collector of phototransistor 91. The total resistance of resistors72 and 73 of the voltage divider network 71 is selected to establish aminor conventional current flow through the solenoid coil 58. The minorvoltage through the solenoid coil 58 is insufficient to actuate thedisconnect switch 50.

The voltage divider circuit 83 of the secondary circuit 80 providesoperating voltage to the light emitting diodes 92 and 93. The lightemitting diodes 92 and 93 are connected through conductor 84 to theshield 48 surrounding the second wire 42 and connected through conductor85 to the shield 47 surrounding the first wire 41.

In the absence of a leakage current between the first wire 41 and thesurrounding shield 47 and the absence of a leakage current between thesecond wire 42 and the surrounding shield 48, the light emitting diodes92 and 93 will not illuminate the phototransistor 91 of the optocoupler90. The absence of illumination of the phototransistor 91 will keep thegate of the thyristor 76 in a low voltage condition. The pull downresistor 78 and capacitor 79 in combination with the coil 77 preventsinadvertent actuation of the thyristor 76 by electrical transients. Aslong as thyristor 76 is in a non-conductive condition, the disconnectswitch 50 remains in the closed or reset condition.

FIG. 14 is the circuit 10 of FIG. 13 with a leakage current R1established between the first wire 41 and the shield 47. Preferably, thevoltage divider circuit 83 establishes a threshold for the leakagecurrent R1 to be less than 0.001 amperes but it should be understoodthat the threshold for the leakage current R1 may be established at anysuitable value. When a positive half-cycle of AC voltage is present onthe first wire 41, conventional current flows from the first wire 41through the leakage resistor R1 through light emitting diode 92 to thevoltage divider circuit 83. When a negative half-cycle of AC voltage ispresent on the first wire 41, conventional current flows from thevoltage divider circuit 83 through light emitting diode 93 to the firstwire 41 through the leakage resistor R1.

If a leakage current (not shown) develops between the second wire 42 andthe shield 48, the circuit 10 undergoes the following current flows.When a positive half-cycle of AC voltage is present on the first wire41, conventional current flows from the voltage divider circuit 83through light emitting diode 93 to the second wire 42 through theleakage resistor R. When a negative half-cycle of AC voltage is presenton the first wire 41, conventional current flows from the second wire 42through the leakage resistor R through light emitting diode 92 to thevoltage divider circuit 83.

The leakage current between the first wire 41 and the shield 47 isconducted through one of the light emitting diodes 93 and 94. Theconduction of the leakage current through one of the light emittingdiodes 93 and 94 illuminates the phototransistor 91. Upon illumination,of the phototransistor 91, phototransistor 91 conducts conventionalcurrent from the collector to the emitter. Upon the conduction of thephototransistor 91, the charge on capacitor 75 flows throughphototransistor 91 raising the voltage on the gate of the thyristor 76to institute conduction of the thyristor 76. The conduction of thethyristor 76 results in a major conventional current flow through thesolenoid coil 58. The major conventional current flow through thesolenoid coil 58 actuates the plunger 59 to open the disconnect switch50 as shown in FIG. 9.

FIG. 15 is the circuit 10 of FIG. 14 illustrating the disconnection ofthe power source 15 from the load 30 upon the opening of the disconnectswitch 50. The opening of the disconnect switch 50 completely isolatesthe power source 15 from the load 30. The optical coupling between thephototransistor 91 and the light emitting diodes 82 and 93 completelyelectrically isolates the primary circuit 70 from the secondary circuit80.

FIG. 16 is the circuit 10 of FIG. 12 illustrating the operation of theoptional test circuit 100. A momentary depression of momentary switch102 causes conventional current flow to flow from the second wire 42through resistor 101 and conductor 103 to the shield 47. Since theshield numeral 47 is connected to the shield 48 by the connector 85, theclosing of the switch 102 creates a current between the second wire 42and the shield 48.

The current between the second wire 42 and the shield 48 is conductedthrough the one of the light emitting diodes 92 and 93 to illuminate thephototransistor 91. The conduction of phototransistor 91 institutesconduction of the thyristor 76 resulting in a major conventional currentflow through the solenoid coil 58. The major conventional current flowthrough the solenoid coil 58 actuates the plunger 59 to open thedisconnect switch 50 as shown in FIG. 9. The circuit 10 may be return toclosed and reset position by the depression of the reset button 82.

FIG. 17 is a circuit diagram of a second embodiment of the circuit 110of FIG. 14. Similar parts are labeled with similar reference numeralsraised by the number 100. In this example, the electrical power source115 is shown as a conventional 220 volt alternating current (AC) powersource. Although the electrical power source 115 has been shown asconventional 220 volt alternating current (AC) power source, it shouldbe appreciated by those skilled in the art that the present inventionmay be adapted to virually any type of power source.

In this example, a voltage dropping resistor 167 is inserted in seriesbetween the first wire 141 and diode 168. In this example, the voltagedivider network 171 is formed from resistor 172 and zener diode 173. Thecombination of the voltage dropping resistor 167 and the voltage dividernetwork 171 comprising resistor 172 and zener diode 173 provides a minorconventional current through solenoid coil 158 to supply a collectorvoltage for the phototransistor 191. The operation of the secondembodiment of the circuit 110 is essentially identical to the operationof the first embodiment shown in FIGS. 3-16.

FIG. 18 is a circuit diagram of a third embodiment of the circuit 210 ofFIG. 14. In this embodiment of the invention the disconnect switch 250is interposed between the source 215 and the load 230. The primarycircuit 270 received operating power from a primary side or source sideof the disconnect switch 250 by conductors 271 and 272. The secondarycircuit 280 received operating power from a secondary side or load sideof the disconnect switch 250 by conductors 281 and 282. The secondarycircuit 280 is optically connected to the primary circuit 270 by theoptocoupler 290.

In this example a conductor 292 connects a sensor 294 to the secondarycircuit 280. The sensor 294 senses any leakage from either the first orthe second wires 241 and 242. The sensor 294 may be the ground wirenormally included in a conventional 110 volt alternating current powercord.

When the sensor 294 senses a leakage from either the first or the secondwires 241 and 242, the secondary circuit 280 optically actuates theprimary circuit 270 for opening the disconnect switch 250. Thedisconnect switch 250 may be any type of appropriate switch fordisconnecting the source 215 from the load 230 including electrical,electronic or electrical-mechanical switches.

FIG. 19 is a circuit diagram of a fourth embodiment of the circuit 310of FIG. 14. In this embodiment of the invention the disconnect switch350 is interposed between the source 315 and the load 330. The primarycircuit 370 received operating power from a primary side or source sideof the disconnect switch 350 by conductors 371 and 372. The secondarycircuit 380 received operating power from a secondary side or load sideof the disconnect switch 350 by conductors 381 and 382. The secondarycircuit 380 is optically connected to the primary circuit 370 by theoptocoupler 390.

In this example a conductor 392 connects a sensor 394 to the secondarycircuit 380. The sensor 394 senses any leakage from the load 330. Whenthe sensor 394 senses a leakage from the load 330, the secondary circuit380 optically actuates the primary circuit 370 for opening thedisconnect switch 350.

FIG. 20 is a circuit diagram of a fifth embodiment of the circuit 410 ofFIGS. 1-4. Similar parts are labeled with similar reference numeralsraised by the number 400. In this embodiment, the primary circuit 470and the secondary circuit 480 of the circuit are located on thesecondary side of the switch 440. The secondary side of switch 440 islocated between the switch 440 and the load 430. The remainder of thefifth embodiment of the circuit 410 is essentially identical to thefirst embodiment of the circuit 10 shown in FIGS. 3-16.

This circuit 410 is may be used where it is desirable to have theprimary circuit 470 and the secondary circuit 480 disconnected from thepower source 420 upon the opening of the switch 440. The operation ofthe second embodiment of the circuit 110 is similar to the operation ofthe first embodiment shown in FIGS. 3-16.

The disconnect switch 450 defines a primary side 450P connected to thepower source 415 and a secondary side 450S connected to the load 430.The nornally open disconnect switched 450 is mechanically closed toconnect the first and second terminals 421 and 422 to the first andsecond wires 451 and 452 of the wire assembly 450.

Upon the application of power, conventional current flows from thesecondary side 450S of the disconnect switched 450 through the solenoidcoil 458 to the voltage divider network 471 to provide a direct current(DC) voltage for the primary circuit 470 and to the collector ofphototransistor 491 of the optocoupler 490.

The voltage divider circuit 483 of the secondary circuit 480 isconnected to the secondary side 450S of the disconnect switched 450 toprovide operating voltage to the light emitting diodes 492 and 493. Thelight emitting diodes 492 and 493 are connected through conductor 484 tothe shields 447 and 448.

In the absence of any leakage current between the either of the firstand second wires 441 and 442 the respective shields 447 and 448, thelight emitting diodes 92 and 93 will not illuminate the phototransistor491 of the optocoupler 490. The thyristor 476 is maintained in anon-conductive condition, the disconnect switch 450 remains in theclosed or reset condition.

In the presence of the leakage current between the either of the firstand second wires 441 and 442 and the respective shields 447 and 448, thelight emitting diodes 92 and 93 will illuminate the phototransistor 491of the optocoupler 490. The phototransistor 491 of the optocoupler 490causes conduction of the thyristor 476 to open the disconnect switch450. The opening of the disconnect switch 450 completely isolates thepower source 415 from the load 430.

In contrast to the previous embodiments set forth in FIGS. 1-19, uponthe opening of the disconnect switch 440, both the primary circuit 470and the secondary circuit 480 are disconnected from the power source415. Upon the disconnected of the primary circuit 470 from the powersource 415, the primary circuit 470 is incapable of electricallyresetting or closing the disconnect switch 450.

FIG. 21 is a circuit diagram of a fifth embodiment of the circuit 510 ofFIG. 14. In this embodiment of the invention the disconnect switch 550is interposed between the source 515 and the load 530. The primarycircuit 570 received operating power from a primary side or source sideof the disconnect switch 550 by conductors 571 and 572. The secondarycircuit 580 received operating power from a secondary side or load sideof the disconnect switch 550 by conductors 581 and 582. The secondarycircuit 580 is optically connected to the primary circuit 570 by theoptocoupler 590.

In this example a conductor 592 connects a sensor 594 to the secondarycircuit 580. The sensor 594 senses the leakage from either the first orthe second wires 541 and 542. The sensor 594 may be the ground wirenormally included in a conventional 110 volt alternating current powercord.

When the sensor 594 senses a leakage from either the first or the secondwires 541 and 542, the secondary circuit 580 optically actuates theprimary circuit 570 for opening the disconnect switch 550. Thedisconnect switch 550 may be any type of appropriate switch fordisconnecting the source 515 from the load 530 including electrical,electronic or electrical-mechanical switches.

FIG. 22 is a circuit diagram of a sixth embodiment of the circuit 610 ofFIGS. 1-4. In this embodiment of the invention the disconnect switch 650is interposed between the source 615 and the load 630. The primarycircuit 670 received operating power from a primary side or source sideof the disconnect switch 650 by conductors 671 and 672. The secondarycircuit 680 received operating power from a secondary side or load sideof the disconnect switch 650 by conductors 681 and 682. The secondarycircuit 680 is optically connected to the primary circuit 670 by theoptocoupler 690.

In this example a conductor 692 connects a sensor 694 to the secondarycircuit 680. The sensor 694 senses the leakage from the load 630. Whenthe sensor 694 senses the leakage from the load 630, the secondarycircuit 680 optically actuates the primary circuit 670 for opening thedisconnect switch 650.

FIG. 23 is a view of an eighth embodiment of a circuit 710 of thepresent invention illustrating a housing 720 similar to the housing 20shown in FIGS. 1-3 with an alternate empower cable 740 extending fromthe housing 720.

The circuit 710 contained within the housing 720 connects the line lug721, the neutral lug 722 and the ground lug 723 of the housing 720 to afirst and a second wire 741 and 742. In this example, the first andsecond wires 741 and 742 shown as a line wire 741 and a neutral wire 742and a ground wire 743 are located within the power cable 740.

The line wire 741, the neutral wire 742 and the ground wire 743 aresurrounded by insulations 741I-743I in a conventional fashion. A drainwire 744 defines a first and a second portion 745 and 746 and extendsalong the substantial totality of the power cable 740. A conductiveshield 747 surrounds the line wire 741, the neutral wire 742 and thegrounding wire 743. An outer insulating layer 748 is molded about theconductive shield 747.

FIG. 24 is an enlarged sectional view along line 24-24 in FIG. 23illustrating the power cable 740 with the first wire 741, the secondwire 742 and the grounding wire 743 surrounded within the conductiveshield 747. In this embodiment, the drain wire 744 is located within theconductive shield 747. The first portion 745 of the drain wire 744 isnon-insulated and in contact with the conductive shield. The firstportion 745 of the drain wire 744 extends along substantially the totallength of the conductive shield 747. The second portion 746 of the drainwire 744 may or may not be insulated. Furthermore, the first portion 745and the second portion 746 of the drain wire 744 may be two separateelectrically interconnected wires (not shown). Preferably, the drainwire 744 is a thin copper or aluminum wire.

The outer insulating layer 748 establishes a mechanical engagementbetween the first portion 745 of the drain wire 744 and the conductiveshield 747 to provide an electrical connection between the drain wire 44and the conductive shield 747. Preferably, the outer insulating layer748 resiliently urges the conductive shield 747 into mechanicalengagement with the drain wire 744 to provide the electrical connectionbetween the drain wire 744 and the conductive shield 747.

FIG. 25 is a view similar to FIG. 24 illustrating a power cable 740Awith the first wire 741, the second wire 742 and the grounding wire 743surrounded within the conductive shield 747. In this embodiment, thedrain wire 744 is located outside of the conductive shield 747. Theouter insulating layer 748 resiliently urges the drain wire 744 intomechanical engagement with the conductive shield 747 to provide theelectrical connection between the drain wire 744 and the conductiveshield 747.

FIG. 26 is a view similar to FIG. 24 of an alternate embodimentillustrating the power cable 740B having the first wire 741, the secondwire 742 and the drain wire 744. In this embodiment, the drain wire 744is located within the conductive shield 747. The power cable 740 is voidof the ground wire 743 shown in FIGS. 24 and 25. The outer insulatinglayer 748 resiliently urges the conductive shield 747 into mechanicalengagement with the drain wire 744 to provide the electrical connectionbetween the drain wire 744 and the conductive shield 747.

FIG. 27 is a view similar to FIG. 27 of another embodiment illustratingthe power cable 740C having the first wire 741, the second wire 742 andthe drain wire 744. In this embodiment, the drain wire 744 is locatedoutside of the conductive shield 747. The outer insulating layer 748resiliently urges the drain wire 744 into mechanical engagement with theconductive shield 747 to provide the electrical connection between thedrain wire 744 and the conductive shield 747.

It should be appreciated by those skilled in the art that the presentinvention is not limited to the cross-sectional shape of the power cord40 or the specific types of wires and/or insulations described andillustrated herein.

FIGS. 28-31 illustrate various examples of conductive shields 747D-747Gsuitable for use with the present invention. The conductive shields747D-747G are shown as thin conductive materials 796D-796G. Typically,the thin conductive materials 796D-796G of the conductive shields747D-747G are unsuitable for direct connection to the interruptercircuit 10.

The drain wires 744 facilitate electrical connection between theconductive shields 747D-747G and the interrupter circuit 10 of thepresent invention. The first portion 745 of the drain wire 744 extendsalong the length of the power cable 740 for electrically connecting thedrain wire 744 to the conductive shields 747D-747G. The second portion746 of the drain wire 744 provides a suitable conductor for connectionto the interrupter circuit 10.

The use of thin conductive shields 747D-747G, substantially reduces thematerial cost over the use of plural conductive shield surrounding thefirst wire and the second wire of the prior art. Furthermore, the use ofan aluminum material for the conductive shields 747D-747G substantiallyreduces the material cost over the use a copper material.

FIG. 28 is a first example of a conductive shield 747D suitable for usewith any of the configurations of the power cables 740-740C shown inFIGS. 24-27. The conductive shield 747D is urged into mechanical andelectrical contact with the drain wire 744D by the outer insulator 748D.In the alternative, the drain wire 744D may be urged into mechanical andelectrical contact with the conductive shield 747D by the outerinsulator 748D. In this example, the conductive shield 747D is shown asa thin metallic foil 796D such as aluminum foil, copper foil or thelike. Preferably, the thin metallic foil has a thickness of 0.001 to0.005 inches.

FIG. 29 is a second example of a conductive shield 747E suitable for usewith the configurations of the power cables 740A and 740C shown in FIGS.25 and 27. The drain wire 744E is urged into mechanical and electricalcontact with the conductive shield 747E by the outer insulator 748E. Inthis example, the conductive shield 747E is shown as a thin insulatingpolymeric material 795E with a metallic conductive coating 796E locatedon one side of the insulating polymeric material 795E. The metallicconductive coating 796E is located on the side of the insulatingpolymeric material 796E facing the drain wire 744E. One materialsuitable for use as the conductive shield 747E is a polyester filmcovered with an aluminum coating or a copper coating.

FIG. 30 is a third example of a conductive shield 747F suitable for usewith any of the configurations of the power cables 740-740C shown inFIGS. 24-27. The conductive shield 747F is urged into mechanical andelectrical contact with the drain wire 744 by the outer insulator 748.In this example, the conductive shield 747F is shown as a thininsulating polymeric material 765F coated with metallic conductivecoatings 796F and 797F located on opposed sides of the insulatingpolymeric material 795F. The metallic conductive coating 796F faces thedrain wire 744F whereas the metallic conductive coating 797F faces thefirst and second wires 741 and 742.

FIG. 31 is a fourth example of a conductive shield 747G suitable for usewith any of the configurations of the power cables 740A-740C shown inFIGS. 24-27. The conductive shield 7470 is urged into mechanical andelectrical contact with the drain wire 744G by the outer insulator 748G.In the alternative, the drain wire 744G may be urged into mechanical andelectrical contact with the conductive shield 747G by the outerinsulator 748G. In this example, the conductive shield 747G is shown asa thin organic conductive polymer 796G. The Wikipedia encyclopedia listthe common classes of organic conductive polymers as poly(acetylene)s,poly(pyrrole)s, poly(thiophene)s, poly(aniline)s, poly(fluorene)s,polynaphthalenes, poly(p-phenylene sulfide), and poly(para-phenylenevinylene)s. Classically, these compounds are known as polyacetylene,polyaniline, etc. “blacks” or “melanins”. The melanin pigment in animalsis generally a mixed copolymer of polyacetylene, polypyrrole, andpolyaniline.

FIG. 32 is a block diagram of the eighth embodiment of a circuit 710 ofthe present invention shown in FIG. 23. The circuit 710 disconnects theelectrical power source 715 from the load 730 upon the detection of aleakage current within the power cable 740. In this example, theelectrical power source 715 is shown as a conventional 110 voltalternating current (AC) power source. The first terminal 21 is the lineterminal whereas the second terminal 22 is the neutral terminal.Although the electrical power source 12 has been shown as conventional110 volt alternating current (AC) power source, it should be appreciatedby those skilled in the art that the present invention may be adapted tovirtually any type of power source.

The circuit 710 comprises a disconnect switch 750 interposed connectingthe first and second lugs 721 and 722 to the first and second wires 741and 742 of the wire assembly 740. The first and second lugs 721 and 722are engaged with the power source 715.

A primary circuit 770 is connected to the disconnect switch 750 forcontrolling the disconnect switch 750. The primary circuit 770 opens thedisconnect switch 750 upon the secondary circuit 780 sensing at leakagecurrent from one of the first and second wires 741 and 742.

A secondary circuit 780 is located between the disconnect switch 750 andthe load 730 for sensing a leakage current between the one of the firstand second wires 741 and 742 and the conductive shields 747.

An optical switch 790 interconnects the primary circuit 770 and thesecondary circuit 780 for opening the disconnect switch 750 upon thesecondary circuit 780 sensing a leakage current within the wire assembly740 for completely electrically disconnecting the power source 715 fromthe load 730 and completely electrically disconnecting the primarycircuit 770 and the secondary circuit 780.

FIG. 33 is a circuit diagram of the block diagram of FIG. 32. The firstand second terminals 721 and 722 extending from the housing 720 areconnected to an input side of the disconnect switch 750. The output sideof the disconnect switch 750 is connected to the first wire 741 and thesecond wire 742 of the wire assembly 740. The first and second switches751 and 752 of the disconnect switch 750 interconnect the first andsecond terminals 721 and 722 to the first and second wires 741 and 742.The disconnect switch 750 is shown in the closed or reset condition.

An optional ground wire 743 bypasses the disconnect switch 750 andpasses to ground the load 730 in a conventional fashion. A surgesuppressor shown as a metal oxide varistor 126 is connected across thefirst and second terminals 721 and 722.

The primary circuit 770 is located on a primary side of the disconnectswitch 750 for controlling the disconnect switch 750. The primarycircuit 770 opens the disconnect switch 750 upon the secondary circuit780 sensing a leakage current from one of the first and second wires 41and 42 and the conductive shield 747.

The disconnect switch 750 is controlled through the solenoid coil 758 bythe primary circuit 770. A diode 768 providing power through thesolenoid coil 758 of the disconnect switch 750 to a conductor 769 topower the primary circuit 770. The solenoid coil 758 is connected to avoltage divider network 771 comprising resistor 772 and resistor 773. Acapacitor 775 is connected across the resistor 773 of the voltagedivider network 771. The conductor 769 is connected to a switch shown asa thyristor or silicon controlled rectifier 776.

The voltage divider network 771 is connected to the collector of thephototransistor 791 of the optocoupler 790. A coil 777 connects theemitter of phototransistor 791 to the gate of the thyristor 776. A pulldown resistor 778 and a capacitor 779 are connected to the gate of thethyristor 776.

The secondary circuit 780 comprises resistor 781 and 782 forming avoltage divider network 783. The voltage divider network 783 isconnected to light emitting diodes 792 and 793 within the optocoupler790. A connector 784 connects the light emitting diodes792 and 793 tothe second portion 746 of the drain wire 744. The first portion 745 ofthe drain wire 744 extends along substantially the total length of theconductive shield 747. The second portion 746 of the drain wire 744 mayor may not be insulated. Furthermore, the first portion 745 and thesecond portion 746 of the drain wire 744 may be two separateelectrically interconnected wires.

An optional test circuit 800 may be included for testing the circuit710. The optional test circuit 800 comprises resistor 801 connected tothe wire 742 of the wire assembly 740. A momentary switch 802 connectsthe resistor 801 to the shield 747 surrounding the first second wire 741through a conductor 803.

The operation of the circuit 710 in FIG. 29 is set forth below. Thecircuit breaker 750 is shown in the closed position as shown in FIG. 5.Power is applied to the circuit 710 by inserting the first and secondlugs 721 and 722 and the ground lug 723 extending from the housing 720into the electrical receptacle 716 shown in FIG. 1.

Upon the application of power, conventional current flows from diode 768through the solenoid coil 758 to the voltage divider network 771. Thediode 768 in combination with solenoid coil 758 provides a directcurrent (DC) voltage for the primary circuit 770. The conductor 769applies power to the voltage divider network 771 and to the anode of thethyristor 776. The capacitor 775 assists in reducing alternating current(AC) voltage ripple within the voltage divider network 771. The voltagedivider network 771 provides operating voltage to the collector ofphototransistor 791. The total resistance of resistors 772 and 773 ofthe voltage divider network 771 is selected to establish a minorconventional current flow through the solenoid coil 758. The minorvoltage through the solenoid coil 758 is insufficient to actuate thedisconnect switch 750.

The voltage divider circuit 783 of the secondary circuit 780 providesoperating voltage to the light emitting diodes 792 and 793. The lightemitting diodes 792 and 793 transfer voltage through conductor 784 andthe drain wire 744 to appear along substantially the total length of theconductive shield 747.

In the absence of a leakage current between the conductive shield 747and any of the first wire 741, the second wires 742 or the ground wire743, zero current will flow through the conductive shield 747 and thedrain wire 744 through the light emitting diodes 792 and 793. With zerocurrent flowing through the light emitting diodes 792 and 793, will notilluminate the phototransistor 791. The absence of illumination of thephototransistor 791 will keep the gate of the thyristor 776 in a lowvoltage condition. The pull down resistor 778 and capacitor 779 incombination with the coil 777 prevents inadvertent actuation of thethyristor 776 by electrical transients. As long as thyristor 776 is in anon-conductive condition, the disconnect switch 750 remains in theclosed or reset condition.

In the event of a leakage appearing between the conductive shield 747and any of the first wire 741, the second wire 742 or the ground wire743, the leakage current will flow through the conductive shield 747 andthe drain wire 744 through one of the light emitting diodes 792 and 793.The leakage current will flow through the light emitting diodes 792 and793 illuminates the phototransistor 791. Upon illumination of thephototransistor 791, phototransistor 791 conducts conventional currentfrom the collector to the emitter. The charge on capacitor 775 flowsthrough phototransistor 791 raising the voltage on the gate of thethyristor 776 to institute conduction of the thyristor 776. Theconduction of the thyristor 776 results in a major conventional currentflow through the solenoid coil 758. The major conventional current flowthrough the solenoid coil 758 actuates the plunger 759 to open thedisconnect switch 750. The opening of the circuit breaker 750disconnects the AC power to the power cable 740 and the load 730. Theopening of the disconnect switch 750 completely isolates the powersource 715 from the load 730. The optical coupling between thephototransistor 791 and the light emitting diodes 792 and 793 completelyelectrically isolates the primary circuit 770 from the secondary circuit780.

The test circuit 800 operates in a similar manner by simulating aleakage current between the conductive shield 747 and the second wire742. The test circuit 800 maybe connected to any of the wires 741-743 ofthe power cable 740. A momentary depression of momentary switch 802causes a test current to flow from the second wire 742 through resistor801 and conductor 803 to the shield 747. The test current is passed bydrain wire 744 through one of the light emitting diodes 792 and 793. Theleakage current through one of the light emitting diodes 792 and 793illuminates the phototransistor 791 to actuate the thyristor 776 to openthe disconnect switch 750 as described previously. The opening of thecircuit breaker 750 disconnects the AC power to the power cable 740 andthe load 730. The opening of the disconnect switch 750 completelyisolates the power source 715 from the load 730.

Although the invention has been shown as a 120 volt single phase systemor a 240 volt single phase system, it should be appreciated that thepresent invention is equally applicable to virtually all single phaseand polyphase systems.

The present invention provide a circuit for disconnecting a power sourceupon the detection of a leakage current that incorporates an improvedconductive shield for the detection of a leakage current. Theincorporation of the improved conductive shield provides a moreeconomical solution than similar units of the prior art. The improvedconductive shield may be incorporated into existing line cord packages.

The present invention has been shown in a preferred form employed withina circuit contained within a housing 20 fashioned in the form of anelectrical plug. However, it should be understood that the presentinvention may be applied to of various types of protection devices forprotecting all types of electrical cords, electrical transmission linesand electrical circuits. Furthermore, the present invention has beenshown with an air conditioning unit 32 as the load 30 but it should beunderstood that the circuit 10 of the present invention is suitable foruse with a large variety of power sources and load as should be apparentto those skilled in the art.

The present disclosure includes that contained in the appended claims aswell as that of the foregoing description. Although this invention hasbeen described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)16. (canceled)
 17. (canceled)
 18. (canceled)
 19. (canceled) 20.(canceled)
 21. (canceled)
 22. (canceled)
 32. A circuit for disconnectinga power source upon the detection of a leakage current, comprising: aleakage current circuit comprising a disconnect switch; a power cableconnected to the power source though said disconnect switch; said powercable consisting of: a. a first insulated wire and a second insulatedwire; b. an insulated ground wire; c. a conductive shield surroundingall of said first and second insulated wires and said insulated groundwire; d. a drain wire having a first and a second portion with saidfirst portion of said drain wire being in contact with said conductiveshield; and e. an outer insulating layer disposed about said conductiveshield and said first portion of said drain wire; and a conductorconnecting said second portion of said drain wire to said leakagecurrent circuit for opening said disconnect switch upon said leakagecurrent circuit sensing a leakage current between said conductive shieldand one of said first and second insulated wires and said insulatedground wire to disconnect said power cable from the power source.
 33. Acircuit for disconnecting a power source upon the detection of a leakagecurrent as set forth in claim 32, wherein said conductive shield is aninsulating polymeric sheet with a metallic coating.
 34. A circuit fordisconnecting a power source upon the detection of a leakage current asset forth in claim 32, wherein said conductive shield is an insulatingpolymeric sheet with an aluminum coating.
 35. A circuit fordisconnecting a power source upon the detection of a leakage current asset forth in claim 32, wherein said conductive shield is a metallicfoil.
 36. A circuit for disconnecting a power source upon the detectionof a leakage current as set forth in claim 32, wherein said conductiveshield is an aluminum foil.
 37. A circuit for disconnecting a powersource upon the detection of a leakage current as set forth in claim 32,wherein said conductive shield is an organic conductive polymericmaterial;
 38. A circuit for disconnecting a power source upon thedetection of a leakage current, comprising: a leakage current circuitcomprising a disconnect switch; a power cable connected to the powersource though said disconnect switch; said power cable consisting of: a.a first insulated wire and a second insulated wire; b. an insulatedground wire; c. a conductive shield consisting of an insulatingpolymeric sheet with a conductive coating surrounding all of said firstand second insulated wires and said insulated ground wire; d. a drainwire having a first and a second portion with said first portion of saiddrain wire being in contact with said conductive coating of saidconductive shield; and d. an outer insulating layer disposed about saidconductive shield and said first portion of said drain wire; and aconductor connecting said second portion of said drain wire to saidleakage current circuit for opening said disconnect switch upon saidleakage current circuit sensing a leakage current between saidconductive coating and one of said first and second insulated wires andsaid insulated ground wire to disconnect said power cable from the powersource.
 39. A circuit for disconnecting a power source upon thedetection of a leakage current as set forth in claim 38, wherein saidconductive coating of said conductive shield is an aluminum coating. 40.A circuit for disconnecting a power source upon the detection of aleakage current, comprising: a leakage current circuit comprising adisconnect switch; a power cable connected to the power source thoughsaid disconnect switch; said power cable consisting of: a. a firstinsulated wire and a second insulated wire; b. a conductive shieldsurrounding both of said first and second insulated wires; c. a drainwire having a first and a second portion with said first portion of saiddrain wire being in contact with said conductive shield; and d. an outerinsulating layer disposed about said conductive shield and said firstportion of said drain wire; and a conductor connecting said secondportion of said drain wire to said leakage current circuit for openingsaid disconnect switch upon said leakage current circuit sensing aleakage current between said conductive shield and one of said first andsecond insulated wires to disconnect said power cable from the powersource.
 41. An improved power cable for use with a leakage currentdetection and interruption circuit for disconnecting a power source uponthe detection of a leakage current within the improved power cable, theimproved power cable consisting of: a. an first insulated wire and asecond insulated wire; b. an insulated ground wire; c. a conductiveshield consisting of an insulating polymeric sheet with a conductivecoating surrounding all of said first and second insulated wires andsaid insulated ground wire; d. a drain wire having a first and a secondportion with said first portion of said drain wire being in contact withsaid conductive coating of said conductive shield; and e. an outerinsulating layer disposed about said conductive shield and said firstportion of said drain wire; and said second portion of said drain wirebeing connected to the leakage current detection and interruptioncircuit for disconnecting the power source upon the detection of aleakage current within the improved power cable between said conductivecoating and one of said first and second insulated wires and saidinsulated ground wire.
 42. An improved power cable for use with aleakage current detection and interruption circuit for disconnecting apower source upon the detection of a leakage current within the improvedpower cable, the improved power cable consisting of: a. an firstinsulated wire and a second insulated wire; b. a conductive shieldconsisting of an insulating polymeric sheet with a conductive coatingsurrounding all of said first and second insulated wires; c. a drainwire having a first and a second portion with said first portion of saiddrain wire being in contact with said conductive coating of saidconductive shield; and d. an outer insulating layer disposed about saidconductive shield and said first portion of said drain wire; and saidsecond portion of said drain wire being connected to the leakage currentdetection and interruption circuit for disconnecting the power sourceupon the detection of a leakage current within the improved power cablebetween said conductive coating and one of said first and secondinsulated wires.